Fuel cell power systems convert a fuel and an oxidant (reactants) to electricity. One type of fuel cell power system employs a proton exchange membrane (PEM) to catalytically facilitate reaction of the fuel (such as hydrogen) and the oxidant (such as air or oxygen) to generate electricity. Water is a byproduct of the electrochemical reaction. The PEM is a solid polymer electrolyte that facilitates transfer of protons from an anode electrode to a cathode electrode in each individual fuel cell of a stack of fuel cells normally deployed in a fuel cell power system.
In the typical fuel cell assembly, the individual fuel cells have fuel cell plates with channels, through which various reactants and cooling fluids flow. Fuel cell plates may be unipolar, for example. A bipolar plate may be formed by combining unipolar plates. The oxidant is supplied to the cathode electrode from a cathode inlet header and the fuel is supplied to the anode electrode from an anode inlet header. Movement of water from the channels to an outlet header is typically caused by the flow of the reactants through the fuel cell assembly. Boundary layer shear forces and a pressure of the reactant aid in transporting the water through the channels until the water exits the fuel cell through the outlet header.
A membrane-electrolyte-assembly (MEA) is disposed between successive plates to facilitate the electrochemical reaction. The MEA includes the anode electrode, the cathode electrode, and an electrolyte membrane disposed therebetween. Porous diffusion media (DM) are positioned on both sides of the MEA to facilitate a delivery of reactants for the electrochemical fuel cell reaction.
Water accumulation within the channels of the fuel cell can result in a degradation of a performance of the fuel cell. Particularly, water accumulation causes reactant flow maldistribution in individual fuel cell plates and within the fuel cell assembly, which can lead to voltage instability that may cause a degradation of the electrodes. Additionally, water remaining in the fuel cell after operation may solidify in sub-freezing temperatures, creating difficulties during a restart of the fuel cell. Water accumulating in the channel regions includes the water byproduct of the electrochemical reaction, liquid water that may accumulate on an inner surface of an inlet flow path for the reactants, and water entrained in the reactant flow streams.
Numerous techniques have been employed to manage water accumulation within the fuel cell. These techniques include pressurized purging, gravity flow, and evaporation, for example. Additionally, the use of water transport structures and surface coatings have been employed that facilitate the transport of water from the channel regions of the fuel cell into an exhaust region of the fuel cell assembly, for example. The methods to manage water accumulation typically focus on removal of water that has accumulated within the channels of the fuel cell and require additional operational steps and/or components for the fuel cell. The additional operational steps and components are known to reduce an efficiency of operating the fuel cell and increase a cost of manufacturing the fuel cell. Liquid water that accumulates on the inner surface of the inlet flow path and water entrained in the reactant flow streams increases a need to employ the various techniques, transport structures, and surface coatings to facilitate removal of water from the channels of the fuel cell.
It would be desirable to produce a cost effective fuel cell stack that minimizes an accumulation of water within a fuel cell and the number of required components to facilitate a removal of water from the fuel cell.